SOLVED: Another misfire chasing threads (2008 express van)

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OR VietVet

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It was a double deuce. Had to flush twice. Love me some tacos. I can eat at least 15 in one sitting but pay the next day. At least, unlike your emoji, I have a toilet! :chewie:
 

ks03

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@Tonyv__ does it happen to run worse if you park it with the front end pointed up an incline?

just thinking 7 and history of 8, if you have oil puddling in your intake it tends to affect those cylinders
 
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Tonyv__

Tonyv__

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@Tonyv__ does it happen to run worse if you park it with the front end pointed up an incline?

just thinking 7 and history of 8, if you have oil puddling in your intake it tends to affect those cylinders
I park in the same spot everyday so I don’t really notice. It seems to be level driveway but if anything it’s sloped toward the street so my front bumper would be inclined down causing oil to go to the front of the motor.

there were s few days I had it on ramps to change transmission pan and fluids. That would be a good incline. I can definitely say I didn’t notice anything to be worse when it came off the ramps.

edit: I also get near all 6 quarts back every 3500 mile oil change too. Idk how much oil I should be losing if there’s a leak/burning somewhere
 
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ks03

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Might have been a little misleading, how I phrased that. I meant while it’s at more of an angle, not necessarily driving after having been at an angle. If there was any puddling in the intake it would exacerbate the issue, because more would run back towards 7 and 8. Accelerating while driving can have the same effect, of moving things back to 7 and 8, but there’s more things going on, an incline could isolate tone potential cause.

depending on how bad or often it acts up it might not take alot of oil to cause it. Intake puddles and oil level could also be mixed with condensation and fuel.
 
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Tonyv__

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hmm. I gotcha. Would I be able to see this if I removed the throttle body and looked inside the intake? I cleaned the TB a few months ago so the gasket should be new enough to remove and reuse? I hope.

also i don’t know if I stated before but the misfire is only noticeable at idle. I can’t tell if I can’t feel it at higher rpms because a v8 has so many other cylinders to pick up the slack or if the misfire isn’t there at higher rpms.

Like for example if I get in my truck and just drive. The code won’t show for days. But I like to warm or cool my truck down. The remote start usually gets the check engine light going because it’s idling for a few minutes or if I spend time sitting in the van the code will come up because I idled too long. So just going off the check engine light I think the mis is only present at idle
 
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Tonyv__

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so I hope I’m not overreacting. But I did a make shift leak test. Cranked cylinder 7 to TDC and hooked up compressed air. It’s hissing through the oil fill hole. Quiet though the TB, exhaust, and antifreeze tank.. However cylinder 8 is doing the same. Didn’t get a chance to check the rest. Free time is at an all time low lately

 

OR VietVet

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When you say you only notice the miss at idle, that leads me to believe a vacuum leak. Before I go further, I want to know the test results of the other 6 cylinders.

With just the two cylinders having air at oil fill: Piston rings bleed by, cracked head/gasket....etc. ?????


A compression test with dry and wet results would help pinpoint.
 
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Tonyv__

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When you say you only notice the miss at idle, that leads me to believe a vacuum leak. Before I go further, I want to know the test results of the other 6 cylinders.

With just the two cylinders having air at oil fill: Piston rings bleed by, cracked head/gasket....etc. ?????


A compression test with dry and wet results would help pinpoint.
So you’re saying piston rings do bleed by?

the video I watched said to hook up air. And listen to 4 places. Air at TB or exhaust would be a valve problem. Bubbles in antifreeze would be headgasket. Or air at oil fill would be rings. However idk how much air or how little.

im getting in over my head. I might have to schedule with Chevy and stop talking about it.

couple years ago I’d spend unlimited hours ripping this thing apart but right now priorities have other Plans for me. This sucks lol
 

OR VietVet

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If left on the air long enough and with enough pressure, you can still get slight air bleed past rings because of piston ring gap, but to do that the air has to go back and forth across the rings till that small gap to get past them. If some idiot built that engine before you got your hands on it, did not stagger the ring gaps and lined them up, well that will allow air past them way easier. If the same amount of air is leaking past all cylinders and you can measure it, then they would be equal enough to drive but compression will blow by them. Even on a great engine, there is very very very slight blow by over time and gets in to the oil. Oil change interval time.
 
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Tonyv__

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Found this tiny vacuum leak with a smoke tester. Could this be big enough to cause rough idle/misfire?
Right above cyl 7
 

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